This invention relates in general to photoconductive elements such as electrophotographic photoreceptors. In particular, this invention relates to photoconductive elements comprising octa-substituted phthalocyanine based pigments which are sensitive to radiation in the infra-red region of the spectrum.
Photoconductive materials have been described as having the ability to generate mobile charge carriers as a result of exposure to actinic radiation or the radiation from solid state sources such as laser diodes and light-emitting diodes in the red or near infra-red portion of the spectrum and to transport them through the bulk of the material. This property has formed the basis for the art of electrophotography, sometimes referred to as "xerography".
Photoconductive elements may comprise a conducting support bearing a layer of a photoconductive material which is insulating in the dark but which becomes conductive upon exposure to actinic or other radiation. A common technique for forming images with such elements is to uniformly electrostatically charge the surface of the element and then imagewise expose it to radiation. In areas where the photoconductive layer is irradiated, mobile charge carriers are generated which migrate to, or away from, the surface of the element and thereby spatially modulate the surface charge. A charge pattern is left behind in non-irradiated areas, referred to as a latent electrostatic image. This latent electrostatic image can then be developed, either on the surface on which it is formed, or on another surface to which it has been transferred, by application of a liquid or dry developer composition which contains finely divided electrostatic marking particles that either are selectively attracted to and deposited in the charged areas or repelled by the charged areas and selectively deposited in the uncharged areas. The pattern of marking particles can be fixed to the surface onto which they are deposited or they can be transferred to another surface and fixed there.
Numerous photoconductor materials have been described as being useful in electrophotography. These include inorganic materials, the best known of which are selenium and zinc oxide, as well as organic materials, monomeric and polymeric, such as arylamines, arylmethanes, azoles, carbazoles, pyrroles, phthalocyanines and the like. For example, U.S. Pat. No. 3,816,118 to Byrne discloses the use of non-substituted metal-free phthalocyanines as photoconductor materials in binder plates; U.S. Pat. No. 3,357,989 to Byrne et al. discloses X-form, metal-free phthalocyanines as photoconductor material in electrophotography; U.S. Pat. No. 4,555,463 to Hor et al. discloses photoresponsive imaging members containing chloroindium phthalocyanine; and U.S. Pat. No. 4,731,312 to Kato et al. discloses photoconductors having a charge generation layer containing indium phthalocyanines.
Electrophotographic elements can comprise a single active layer, containing the photoconductive material, or they can comprise multiple active layers. Elements with multiple active layers (sometimes referred to as multi-active elements) have at least one charge generation layer and at least one charge transport layer. The charge generation layer responds to actinic radiation, or radiation in the red and near infra-red region of the spectrum, by generating mobile charge carriers. The charge transport layer facilitates migration of the charge carriers to or from the surface of the element, in order to dissipate the uniform electrostatic charge and form a latent electrostatic image.
The majority of photoconductors described in the art are sensitive to electromagnetic radiation in the ultraviolet, visible, and near infra-red regions of the electromagnetic spectrum as disclosed in U.S. Pat. No. 4,587,189 to Hor et al. However, as information storage and retrieval technology have evolved, increasing use has been made of light emitting devices which emit radiation principally in the near infra-red region of the electromagnetic spectrum, i.e., from about 600 nm to about 900 nm. Many of the previously known photoconductive materials either do not adequately respond to radiation in this region of the spectrum, i.e., they have little or no sensitivity to such radiation, or if they do respond to such radiation, they suffer from other disadvantages. For example, they may have a very large dark conductivity, which limits their ability to accept and hold electrostatic charge, or they may have poor quantum efficiencies, which prevent them from making effective use of exposing radiation resulting in low electrophotographic sensitivity, or they may require the application of an extremely high electrostatic charge or the use of other extreme conditions in order to exhibit the useful electrophotographic sensitivity. Additionally, they may require cumbersome or costly manufacturing processes.
An example of a photoconductive element reportedly sensitive in the infra-red region appears in U.S. Pat. No. 4,471,039 to Borsenberger et al. which is directed to photoconductive elements comprising .beta.-phase indium phthalocyanines in the charge generation layer. The phthalocyanines disclosed in Borsenberger et al. may be unsubstituted or have substituents associated with the indium atom or the phthalocyanine rings. Preferred substituents for either the indium atom or phthalocyanine rings are halogen atoms. These photoconductive elements are sensitive to electromagnetic radiation in the infra-red region of the spectrum. Other substituents such as hydroxy, alkoxy, aryloxy, and alkyl may be associated with the indium atom or phthalocyanine rings. However, Borsenberger et al. does not disclose any preferred arrangement for these other substituents for conferring improvements or advantages as in the present invention, nor are they specific as to the nature of any such improvements.
Although there are photoconductive elements which are sensitive to radiation in the infra-red spectrum, there is still a need for photoconductive elements sensitive to the near infra-red region of the electromagnetic spectrum having low dark decay properties, high electrophotographic sensitivity, less sensitivity to property changes induced by environmental shifts in temperature and humidity, and enable improved manufacturability.